The present invention relates to a method of fabricating a part out of thermostructural composite material, in particular of the oxide/oxide type or of the ceramic matrix composite (CMC) type, i.e. comprising fiber reinforcement made of fibers of refractory material and densified with a matrix that is likewise made of refractory material.
Oxide/oxide composite material parts are generally prepared by taking a plurality of fiber plies made from refractory oxide fibers and draping them in a mold, each ply being previously impregnated with a slip filled with refractory oxide particles. The set of plies as arranged in this way is then compacted using a countermold or a vacuum sheet and passing through an autoclave. The filled preform as obtained in this way is then subjected to sintering in order to form a refractory oxide matrix within the preform and obtain a part made out of oxide/oxide composite material. This technique can also be used for making parts out of ceramic matrix composite (CMC) material. Under such circumstances, the fiber plies are made out of fibers of silicon carbide (SiC) or of carbon and they are impregnated with a slip filled with particles of carbide (e.g. SiC), of boride (e.g. TiB2), or of nitride (e.g. Si3N4).
Nevertheless, that type of preparation method is suitable only for making CMC or oxide/oxide composite material parts that are of small thickness and that have two-dimensional (2D) fiber reinforcement. The mechanical characteristics of composite materials of those types remain limited in certain directions. In particular, those materials present poor delamination performance and they do not withstand shear forces well.
Fiber textures obtained by three-dimensional weaving between continuous warp and weft yarns enables the mechanical strength of the material to be increased, and in particular enables its ability to withstand delamination to be increased. Under such circumstances, and also for thick 2D fiber textures, it is possible to cause a filled suspension to penetrate into the fiber texture, which may be of thickness that reaches several tens of millimeters, depending on the intended applications, only by means of methods that make use of a pressure gradient, such as infusion type methods, injection molding type methods known as resin transfer molding (RTM), or methods involving suction of submicron powder known as advanced powder solutions (APS).
Nevertheless, in the context of making a part out of CMC or oxide/oxide material, those methods present certain drawbacks.
Specifically, impregnating a fiber texture of complex shape and great thickness cannot be performed using an infusion type method, since it does not enable a pressure gradient to be reached that is sufficient for obtaining good impregnation throughout the texture.
The APS type method does not provide fine control over the quantity of matrix that is introduced into the preform.
Although the RTM method can be used for impregnating a fiber texture with a filled slip, it nevertheless requires performing a step of eliminating the solvent of the slip (by evaporation and discharge) in order to leave only the solid fillers in the preform prior to sintering. This step of eliminating the solvent is not usually performed when performing an RTM method. This additional step leads to considerably longer times for treating a preform. It can also be necessary to repeat the operation of injecting the slip, and consequently also the operation of eliminating the solvent.
Furthermore, evaporating the solvent is difficult, since the solvent needs to be removed from the preform without disturbing the distribution of solid particles (refractory oxide, carbide, boride, nitride, etc.) that have been deposited by the slip. Specifically, while drying the impregnated preform, evaporating and discharging the solvent can lead to particles being entrained with the solvent and/or can modify the distribution of the particles in the preform and can lead to large pores appearing in the final material because of the lack of matrix at certain locations.